C64-dev/newLang/docs/decisions.md

---

type: project-decisions source-path: user conversation and repository inspection ingested-at: 2026-11-07

Project Decisions

This file prevents later agents from silently changing the approved product. Accepted means the user explicitly requested, confirmed, or approved the documented default. Proposed means a later change still needs approval.

Accepted

ID	Decision	Consequence
D001	Create an object-oriented language for the Commodore 128.	C128 behavior and limits define the platform contract.
D002	Write the compiler in assembly.	Compiler implementation uses documented 8502/6502 instructions and ca65 source.
D003	Source creation must work with the repository's new Vim clone.	The compiler accepts the editor's PETSCII SEQ output directly.
D004	Put project programs and supporting material under newLang/.	Existing vim/ and reference assets remain external inputs.
D005	Plan and obtain approval before implementation.	The user approved continuation on 2026-11-07; implementation stories may now be claimed in dependency order.
D006	Support interfaces.	Interfaces and dynamic interface dispatch are version 1 work, not an optional extension.
D007	Create a specification and epics/stories suitable for other agents.	Work is divided into claimable, testable stories with durable context.
D100	Use Nova128 as the language name and .n8 as the source suffix.	Short, recognizable, and compatible with 16-character disk filenames.
D101	Run the compiler in C128 native 8502 mode.	Gives access to both RAM banks, the MMU, 80-column facilities, and 2 MHz operation where safe.
D102	Use host ca65/ld65 only to build the on-machine compiler.	The resulting compiler still runs entirely on the C128.
D103	Keep the existing Vim binary in C64 mode for version 1.	A native C128 editor port is a separate large project.
D104	Exchange source through a copied D81 image.	It works with the current editor without inventing an editor API.
D105	Use explicit new/delete and a deterministic free-list heap.	Avoids the size and timing cost of garbage collection.
D106	Permit multiple interfaces but no class inheritance in version 1.	Delivers polymorphism while limiting layout and dispatch complexity.
D107	Use statically dispatched concrete method calls and dynamically dispatched interface calls.	Keeps ordinary calls fast while preserving interface polymorphism.
D108	Represent interface values as a four-byte pair: object pointer plus interface-table pointer.	Makes interface invocation constant-time without searching class metadata on every call.
D109	Compile one source file into one PRG in version 1.	Separate compilation and object linking can follow a proven compiler.
D110	Use KERNAL-compatible output so the compiler can operate on 40- or 80-column displays.	Avoids coupling the first compiler UI directly to one video chip.
D111	Physical C128 testing is P2 validation, not a version 1 release blocker when hardware is unavailable.	VICE x128 remains the mandatory automated acceptance environment.
D112	Compiler diagnostics use the active C128 display and do not force 80-column mode.	The compiler remains usable with either display; safe clock acceleration is opportunistic.
D113	Version 1 integer overflow always wraps in the destination representation.	Debug overflow trapping is deferred, keeping semantics identical between builds.
D114	Version 1 has no interface-to-class down-cast operation.	Programs express polymorphism through interfaces without runtime type reflection.
D115	Character literals use single quotes and contain exactly one PETSCII character or supported escape.	The char type has a direct, unambiguous literal form while // remains the comment syntax.
D116	Runtime faults report a stable code and the best available map-resolvable program address.	Rich stack traces are deferred; faults remain diagnosable within the runtime budget.
D117	Freeze the compiler memory map in cfg/compiler.cfg: 8K bottom common RAM, COMMON at $1300, private zero page at bank 0 page $1A via P0, bank-1 tables at $2000-$BFFF, IRQs masked and NMIs guarded in compiler states, test mailbox at $1BF0.	Internal contract backed by E01-S05 x128 evidence (docs/memory-map.md); no user-visible behavior except that RESTORE is ignored while compiling. Generated-program maps remain open.
D118	The compiler loads the whole source file once into a bank-1 cache ($2000-$6AFF) and replays it for every pass, instead of re-reading the disk.	Rewind is exact by construction and avoids reading a slow disk three times. Compiler tables get the remaining 21,760 bytes of bank 1 ($6B00-$BFFF). Internal; no user-visible behavior.

Proposed

ID	Proposal	Consequence
D119	The string and character escapes \n and \r both produce PETSCII $0D.	Commodore output has one line-end character, so both escapes start a new line. Implemented as ESC_N_VALUE/ESC_R_VALUE in src/common/tokens.inc; changing them later affects only those constants and the lexer golden files.

Deferred

• Native C128/80-column Vim port
• Vim :make and error-navigation commands
• Class inheritance and virtual class methods
• Interface inheritance and default methods
• Separate compilation and relocatable Nova128 object files
• Garbage collection or reference counting
• Exceptions, generics, closures, reflection, and method overloading
• Floating point
• C64 and Z80 code-generation targets
• Bank 1 heaps for generated programs

Open Questions

1. What generated-program memory map should E04-S01/E04-S02 adopt? (The compiler map is D117.)
2. What compiler table capacities fit in the 21,760-byte bank-1 table window and 254-byte zero page (D117, D118)?